EP0811309A1

EP0811309A1 - Method for making a heat conduction-cooled electronic card

Info

Publication number: EP0811309A1
Application number: EP96902303A
Authority: EP
Inventors: Vito Suppa; Noel Begnis; Jean-Claude Aldon
Original assignee: Thomson CSF SA
Current assignee: Thales SA
Priority date: 1995-02-21
Filing date: 1996-01-30
Publication date: 1997-12-10
Also published as: US6035524A; FR2730894A1; WO1996026631A1; CA2212943A1; FR2730894B3

Abstract

Methods for making thermally cooled electronic cards are disclosed. The method comprises providing a card (2, 3i) of any kind to be covered with a rigid heat sink (1) shaped to fit and attached to the card (2, 3i), and forming said heat sink (1) in such a way that it fits as closely as possible the shape of the printed circuit (2) having components (3i) on one or both sides thereof, whereby the surface thermal coupling between the sink (1) and the card (2, 3i) may be increased, by means of an optical sensor which preferably operates with a laser beam. Such a heat sink may thus be manufactured more quickly.

Description

METHOD FOR MANUFACTURING AN ELECTRONIC CARD HAVING THERMAL CONDUCTION

The present invention relates to the field of heat dissipation of electronic components on printed circuits and more particularly relates to a method of manufacturing an electronic card cooled by thermal conduction.

In the electronic components sector, integrated circuits are becoming smaller and smaller while performing increasingly complex functions. The increase in the integration density leads to an increase in the thermal density dissipated in the boxes containing the electronic cards, the physical dimensions of which always remain of the same order of magnitude. Problems then arise in evacuating the energy dissipated as heat during their operation. It follows that, as the dimensions of the integrated circuits decrease, the resolution of the problems posed by heat dissipation becomes more and more difficult and costly. Due to economic problems, the electronic industry, mainly military in application, has turned to the civilian industrial sector. Currently, there is a strong expansion of electronic equipment in the civil industrial sector, which today competes, in functional terms, with certain military equipment.

To use cards originally designed for civilian use, there are then more severe environmental and climatic constraints in the military than in the civilian sector.

Manufacturers of electronic components always specify a maximum operating temperature above which the characteristics of the component are no longer guaranteed. Depending on the function of the component and its field of application, the maximum temperature varies from + 70 ° C for the industrial range to + 125 ° C for the military range. The use of components originally intended to operate at a maximum temperature of 70 ° C and intended to operate at a higher temperature requires local cooling of the electronic card fitted with the components.

Local cooling makes it possible to maintain an operating temperature compatible with the maximum admissible temperature for normal use of the card.

It is known, to promote the heat dissipation of components wired on a printed circuit board, to use a conduction heat transfer device placed between the components and the cover of the metal case enclosing the card equipped with the components, the cover being used as a dissipating cold plate.

In a known embodiment, a plasticized bag containing a coolant of the fluoradiator type is used; a bag of this type is sold under the trade name of FLUORINERT.

Such a heat dissipation device is difficult to implement in devices containing multiple cards such as, for example, card bins equipping bay structures. Indeed, the cards are generally positioned vertically inside the tray and the reduced space between cards does not allow a cold dissipative plate to be inserted. On the other hand, due to the vertical position of the cards, a device of the cooler bag type would no longer be held on the card. Finally, the bag type device has a certain rigidity and is only applied on top of the electrical components which emerge the most from the printed circuit board. The interface between the components and the bag is not optimized. Thus, some of the components which are not in contact with the bag cannot be cooled sufficiently to allow them to operate within the temperature ranges specified for military applications. This excludes from these applications the cards thus equipped.

To resolve this problem and allow the use of any commercial card for military uses, the applicant described in French patent application No. 92 06 041 filed on May 19, 1992 and published on November 26, 1993 under the No. ° 2 691 604, a process consisting in forming on any card fitted with components a rigid heat sink, fixed to the card, closely matching the components and thus allowing their cooling even for the highest temperatures of the military range, the card can be used in materials comprising card bins.

For this, this method uses a system for monitoring the face comprising the electronic components, or an imprint of this face, which uses a mechanical sensor whose precision, robustness, and scanning speed are low.

To overcome these drawbacks, the invention provides a method of manufacturing an electronic card with thermal conduction cooling, this card comprising a printed circuit on which electronic components are fixed on at least one of the faces of the printed circuit, this circuit being associated with a heat dissipation device, in which:

an impression is made of the face of the printed circuit equipped with the components,

- the imprint is followed by a position sensor to describe its entire surface,

- the position information from the sensor is converted and processed using a computer system in order to constitute a machining program,

- from the machining program, a rigid heat sink is machined with a programmable machine tool, one face of which is adapted to closely match the face of the printed circuit equipped with the components

the surface of the printed circuit equipped with the components is covered by the heat sink, and

- the heat sink is mechanically fixed on the printed circuit equipped with the components; this method being mainly characterized in that the position sensor comprises a laser scanning head making it possible to obtain the coordinates of the different points of said face.

According to another characteristic, savings are made in the drain allowing access to certain parts of said face and / or components that it supports. According to another characteristic, the position sensor is forwarded directly to the face of the printed circuit equipped with the components.

According to another characteristic, the drain is provided with a liquid circulation system making it possible to cool this drain. According to another characteristic, this circulation system is of the serpentine type.

According to another characteristic, the drain is joined to the electrical ground of the card to shield this card from an electromagnetic point of view. According to another characteristic, the drain is extended to the edges of the card, and the edges of this drain are thinned to allow them to be inserted in the card holding slides, which makes it possible to use thermal type.

Other features and advantages of the invention will appear clearly in the following description, presented by way of nonlimiting example and made with reference to the appended figures which represent:

- Figure 1a, a sectional view of the assembly of a heat sink produced according to the method according to the invention, with a printed circuit equipped with components; - Figure 1b, the sectional view of the previous assembly completed with a material providing the interface between the drain and the printed circuit equipped with components;

- Figure 1 c, the sectional view of the previous assembly with a drain made according to a variant of the invention; - Figure 2, an impression of an electronic card;

- Figure 3, a first embodiment of the method according to the invention;

- Figure 4, a second embodiment of the method according to the invention; and - Figure 5, an alternative embodiment of the invention.

In the following description, the elements common to each of the figures are identified by the same reference.

FIG. 1 a illustrates a sectional view of a thermal cooling electronic card manufactured according to the method according to the invention. This card includes an assembly of a heat sink 1 with a printed circuit 2 equipped with electronic components 3i. The face 4 of the heat sink 1, facing the components 3i, exactly follows the face 5 of the printed circuit 2 equipped with the components 3i and just fits thereon. The two faces, 4 and 5, are separated by an empty space 6 of a few tenths of a millimeter corresponding for example to the thickness of a film described later.

The space 6 is advantageously used on the one hand to ensure thermal coupling between the drain 1 and the printed circuit 2 and on the other hand to ensure mechanical coupling by fixing the drain 1 on the printed circuit 1 equipped with the components 3i. As shown in the sectional view of FIG. 1b, the mechanical and thermal coupling is carried out by one or more materials 7 independently or jointly ensuring the functions of electrical insulator and good thermal conductor, and which can be adhesive. This material can for example be a putty, a resin, a varnish, a grease, or a gel, inserted between the face 4 of the drain 1 and the face 5 of the printed circuit 2 equipped with the components 3i. The materials 7 completely fill the space 6 and thus ensure a surface thermal coupling without heat accumulation points. The heat sink 1 thus fixed on the printed circuit 2 also ensures the tightness of the electronic card, 2 and 3i, in particular with respect to water vapor. The materials 7 used to ensure the thermal and mechanical couplings can be dissolved by a solvent suitable for the materials 7 or mechanically destroyed to allow disassembly of the drain 1 in the event of intervention on the electronic components 3i implanted on the printed circuit 2.

This heat sink 1 also guarantees better mechanical rigidity of the card. It can therefore also be considered as a mechanical stiffener. In addition, the heat sink can be connected to an electrical potential reference, the ground of the card for example, to allow it to play the role of electromagnetic screen. This protection is particularly effective in solving electromagnetic compatibility problems between neighboring cards in the same bin. As shown in the sectional view of FIG. 1c, the face 8 of the heat sink 1 opposite the components 3i can be advantageously profiled.

It is for example fitted with notches 9i, of the radiator fin type, thus making it possible to increase the heat exchange by convection between the heat sink 1 and the ambient air.

FIG. 2 illustrates a first step of a first embodiment of the method according to the invention, in which an impression is taken of the face 5 of the printed circuit 2 and of the components 3i implanted on the printed circuit 2. A any card, 2 and 3i, of the trade, consisting of the printed circuit 2 and the components 3i installed on the printed circuit 2, may be temporarily coated with a film 10 of thin thickness, for example of the order of 0.5 mm . The film 10 is made of a rigid thermoformable and preferably antistatic material to prevent any electrostatic discharge which can destroy certain fragile components in contact with the film 10.

To deform the film 10, an example of a known technique consists in softening the film 10 produced in a thermoplastic material, for example a material of the Macrolon (registered trademark) type, polycarbonate, PVC, etc., under the action of a source. of heat and at the same time, sucking the film 10 towards the components 3i by creating a vacuum, ie a partial vacuum between the film 10 and the printed circuit 2.

The film 10 thus closely follows the shape of the components 3i and can join in places the surface of the printed circuit 2 in the widest spaces between components 3i. Once cooled, the film 10 retains the deformation undergone by the previous operation in the form of an imprint, in fact corresponding to the softened relief, or smoothed, of the real relief presented by the components 3i distributed over the surface of the printed circuit 2 .

From the imprint of the relief, possibly materialized by the film 10 as previously described, a second step of the first embodiment of the method according to the invention, illustrated by FIG. 3, consists in forming the heat sink 1 adapted to the map, 2 and 3i, of which the impression was made, to use a position sensor (XYZ) 11. According to the invention, the height dimension Z is obtained using an optical probe operating at from a laser beam 110. This sensor traverses the surface of the film 10, or of the card, and transmits the three-dimensional information (XYZ) of position to a programmable machine tool 12 in the form of a machining program 13. This sensor can in particular be formed by a scanning head such as those which are used in a known manner in integrated machining systems. The distance is measured in a known manner by triangulation. To facilitate tracking by the laser beam in the case where the film 10 is not used, the surface of the card comprising the components can be dusted with a white powder which allows correct back scattering of the laser beam.

The heat sink 1 is machined from a rigid material which is a good thermal conductor, for example an aluminum alloy, and thus constitutes the "negative of the face 5 of the printed circuit 2 equipped with the components 3i.

In a particular variant embodiment, savings are made in the drain, that is to say holes, allowing access to certain parts of said face (5) and / or of the components which it supports.

In particular applications, such as missiles or torpedoes, the point of thermal equilibrium between the heat sink and the ambient environment is not reached in the very short period of use of the card (transient use). The heat sink used then serves as a heat reservoir.

Aluminum is a material with a high caloric storage power. In addition, a heat sink made of an aluminum-based material can be arranged to receive materials with solid / solid phase change, such as acetamide, or liquid / vapor such as methanol. These materials, in the form of inserts are placed in the thickness of the thermal drain and thus make it possible to increase the heat capacity of the thermal drain.

In addition, one can include within the drain thus produced a liquid circulation system, for example a coil, which allows cooling by circulation of a liquid coming from an external source.

One can also advantageously machine the edges 16 of the drain, so as to thin them, for example to a thickness of 5 tenths of millimeter, to be able to extend them vertically to the edges of the substrate 2 of the card.

In this way, the edges of the drain will be able to slide, like those of the card, in the slides for holding it in the tray intended to receive it. We can then use for these slides so-called "thermal" models. These thermal slides, known in themselves, make it possible to cool the sides of the card, and therefore of the drain, by transferring the calories from the drain to a heat sink outside the card. This heat sink may for example be a cold plate forming part of the tray receiving the cards and comprising these slides. This system, which can also operate at the connector of the card, is described in particular in French patent application No. 89 09638 filed by the applicant on July 18, 1989 and published on January 25, 1991 under No. 2,650,146. A second embodiment of a heat sink according to the invention, illustrated by FIG. 4, consists in directly raising the profile 14, materialized by a dotted line, from the face 5 presented by the printed card 2 and the components 3i to describe the entire surface of face 5 without passing through the film 10. The position sensor 15 is studied to tangent the profile 14. The processing of position information (XYZ) then being identical to that of the first embodiment, it will therefore not be described again. To keep the space 6 corresponding, in the previous embodiments, to the thickness of the film 10 and allowing mechanical and thermal coupling between the drain 1 and the printed circuit 2 equipped with the components 3i, it suffices to provide in the program machining 13 an offset, for example of 0.5 mm, between the real profile 14 raised by the sensor 15 and the profile to be machined corresponding to the face 4 of the drain 1, and a smoothing subroutine making it possible to obtain reliefs neither too narrow nor too sharp. The last step of the process according to the invention then consists in covering the printed circuit and the components 3i implanted on the circuit 2 by the thermal drain 1 produced according to one of the preceding embodiments and in mechanically fixing the drain 1 on the card , 2 and 3i, through the material 7 filling the space 6 between the drain 1 and the card, 2 and 3i, for ensure mechanical and thermal coupling between drain 1 and the card, 2 and 3i.

The invention is not limited to the precise description of the preceding embodiments: In particular, all the materials constituting the drain, the film as well as the interface between the drain and the electronic card equipped with the components, having the useful characteristics to the invention, fall within the scope of the present invention.

Similarly, the invention is not limited to a printed circuit on one side and can also extend to a printed circuit on both sides, the card then comprising a heat sink on either side of the printed circuit. .

Claims

1. Method for manufacturing an electronic card cooled by thermal conduction, this card comprising a printed circuit (2) on which electronic components (3i) are fixed to at least one of the faces of the printed circuit, this circuit being associated with a heat dissipation device (1), in which:

- an imprint is formed of the face (5) of the printed circuit (2) equipped with the components (3i), - the imprint is followed by a position sensor (11; 15) to describe its entire surface,

- the position information (XYZ) from the sensor (11, 15) is converted and processed using a computer system in order to constitute a machining program (13), - from the machining program (13), we machine with a programmable machine tool (12). a rigid heat sink (1), one face (4) of which is adapted to closely match the face (5) of the printed circuit (2) equipped with the components (3i),

the surface (5) of the printed circuit (2) fitted with the components (3i) is covered by the heat sink (1), and

- The heat sink (1) is mechanically fixed to the printed circuit (2) fitted with the components (3i); this method being characterized in that the position sensor (11, 15) comprises a laser scanning head making it possible to obtain the coordinates (X.Y.Z) of the different points of said face (5).

2. Method according to claim 1, characterized in that what is spared in the savings drain allowing access to certain parts of said face (5) and / or the components which it supports.

3. Method according to any one of claims 1 and 2, characterized in that the position sensor (11, 15) is forwarded directly the face (5) of the printed circuit (2) equipped with the components (3i) .

4. Method according to any one of claims 1 to 3, characterized in that one provides the drain (1) with a liquid circulation system for cooling this drain.

5. Method according to claim 4, characterized in that the circulation system is of the serpentine type.

6. Method according to any one of claims 1 to 5, characterized in that the drain (1) is joined to the electrical ground of the card (2) to shield this card from an electromagnetic point of view.

7. Method according to any one of claims 1 to 6, characterized in that one extends the drain (1) to the edges of the card (2), and that one thins the edges (16) of this drain to allow them to fit into the card holding slides, which allows the use of thermal type slides.